Mechanism for cross-linking polychloroprene with ethylene thiourea and zinc oxide

An investigation into the mechanism by which ethylene thiourea (ETU) cross-links polychloroprene (CR) in combination with zinc oxide (ZnO) was undertaken. This was achieved through an examination of the mechanisms of crosslinking CR with ETU and ZnO separately and in unison. Spectroscopic and physical characterization techniques were employed to probe the cross-linking mechanisms of CRusing other standard rubber accelerators and model compounds with analogous structures and functionalities to ETU. These investigations have resulted in the proposal of a new mechanism by which ETU and ZnO can synergistically cross-link CR, in addition to providing new evidence to support concomitant mechanisms already published for cross-linking CR.

Avaliação da influência de diferentes óleos extensores com baixo teor de policíclicos aromáticos nas propriedades da borracha à base butadieno e estireno (SBR)

O óleo extensor normalmente empregado em copolímeros à base de butadieno e estireno ( borracha SBR) da série 1712 é o extrato aromático (DAE). Nesta Dissertação, esse óleo foi substituído por óleos com baixos teores de policíclicos aromáticos em formulações de SBR. Esta substituição se deu em atendimento a Regulamentação REACH (EC No1907/2006 do Parlamento Europeu e do Conselho de 18 de Dezembro de 2006, Anexo XVII) que determina que a soma de hidrocarbonetos policíclicos aromáticos individuais (PAHs) deve ser abaixo de 10 mg/kg e o teor de benzo(a)pireno (BaP) não deve exceder 1 mg/kg. Os óleos empregados foram o extrato aromático residual tratado (TRAE) e dois óleos naftênicos de fornecedores diferentes (HN1 e HN2). As composições de SBR estendidas em DAE, TRAE, HN1 e HN2 tiveram suas propriedades térmicas avaliadas por análise termogravimétrica (TG) e calorimetria diferencial de varredura (DSC). As propriedades físicas foram determinadas por ensaios de tração, dureza, resistência à abrasão e resiliência. Foram ainda avaliadas as propriedades reométricas e reológicas, por viscosidade e relaxação Mooney, respectivamente. Ao final os resultados demonstraram que é possível a substituição do óleo extensor por quaisquer dos óleos testados sem prejuízos nas propriedades estudadas

Avaliação da biodegradabilidade de filmes de polihidroxibutirato com borracha natural

A modernidade exige materiais versáteis, resistentes e, durante um longo tempo os plásticos serviram a esse propósito. Entretanto, o acúmulo desses materiais ao serem descartados no meio ambiente tornou-se um problema Os polímeros biodegradáveis surgiram neste cenário como alternativa para evitar o acúmulo de resíduos plásticos no meio ambiente. O polihidroxibutirato (PHB) representa uma classe de polímeros biodegradáveis, mas que apresenta um alto custo e possui ainda propriedades térmicas limitadas. A borracha natural possui excelentes propriedades mecânicas, resistência ao envelhecimento, flexibilidade e apresenta melhor custo benefício se comparada com as borrachas sintéticas. Neste estudo, foram elaboradas misturas poliméricas de polihidroxibutirato (PHB) e látex de borracha natural em diferentes concentrações, por prensagem à quente. Os ensaios de calorimetria diferencial de varredura (DSC), análise termogravimétrica (TGA), espectrometria na região do infravermelho (FTIR), microscopia ótica (MO) e microscopia eletrônica de varredura (MEV) foram utilizados para caracterizar e avaliar as propriedades das misturas poliméricas. O PHB e as misturas com borracha natural foram submetidos ao ensaio de biodegradabilidade através do enterro em solo simulado, conforme a norma ASTM G 160-03, variando por um período de 2 a 17 semanas. Ao final de cada período foram determinadas a perda de massa, a morfologia dos corpos de prova e foram realizadas as análises de DSC, TGA e FTIR. As misturas poliméricas apresentaram menor resistência térmica do que o PHB. No ensaio de biodegradabilidade, as misturas foram consideradas biodegradáveis, segundo a norma ASTM G 160-03 e tiveram a porcentagem de cristalinidade reduzida, tendo o teor de borracha natural contribuído para aumentar a taxa de biodegradação. As análises por MEV comprovaram a existência de consórcios de microrganismos, responsáveis pela biodegradação do PHB e das misturas poliméricas

Monitoring bioaccumulation and toxic effects of hexachlorobenzene using the polyurethane foam unit method in the microbial communities of the Fuhe River, Wuhan

Hexachlorobenzene (HCB) is a chlorinated aromatic hydrocarbon that was widely used for seed dressing in prevention of fungal growth on crops, and also as a component of fireworks, ammunition, and synthetic rubbers. Because of its resistance to degradation and mobility, HCB is widely distributed throughout the environment and is accumulated through food chains in different ecosystems. In this study, a preliminary investigation was carried out on the bioaccumulation and the toxic effects of HCB in the microbial (protozoan in particular) communities in the Fuhe River, Wuhan, a water body receiving industrial wastewaters containing HCB and other pollutants, using the standardized polyurethane foam units (PFU) method. Field samples were taken from eight stations established along the Fuhe River in January and August 2006. The concentration ratios of HCB in microbial communities and in water were 9.66-18.64, and the microbial communities accumulated 13.29-56.88 mu g/L of HCB in January and 0.82-10.25 mu g/L HCB in August. Correlation analysis showed a negative correlation between the HCB contents in the microbial assemblage, and the number of species and the diversity index of the protozoan communities. This study demonstrated the applicability of the PFU method in monitoring the effects of HCB on the level of microbial communities.

UNSTEADY DIFFUSION KINETICS OF ZIEGLER-NATTA HETEROGENEOUS CATALYST POLYMERIZATION .4. PREDICTION OF EXPERIMENTAL RESULTS OF PROPYLENE ETHYLENE 1-HEXADECENE TERPOLYMERIZATION

The prediction, based on unsteady diffusion kinetics, of the enhancement of reactivity and incorporation of 1-hexadecene in its copolymerization with propylene on adding a small amount of ethylene (increase from 5,2 mol-% to 10,8 mol-% when 2% of ethylene was added, and to 16,1 mol-% when 5% was added) was verified in the terpolymerization of propylene/1-hexadecene/ethylene on a commercial Solvay-type delta-TiCl3 catalyst. The catalyst efficiency was thus also increased. These augmentations originate from the increase in diffusion coefficient of 1-hexadecene at the catalyst surface when the PP crystallinity decreases on introduction of ethylene. Calculation based on unsteady diffusion kinetics showed that the order of diffusion coefficients ethylene > propylene > 1-hexadecene is reversed as the monomer concentration increases when the monomers are not at their equilibrium concentration. Sequence distribution as determined by means of C-13 NMR revealed a tendency of blocky structure rather than a Bernoullian one. The terpolymer compositions obtained by means of an IR method developed in this work conform rather well with the NMR results. Results in this work not only support the unsteady diffusion kinetics but also provide a new route to prepare olefinic copolymer rubbers with heterogeneous titanium catalysts.

Multilayer mirrored bubbles with spatially-chirped and elastically-tuneable optical bandgaps

We demonstrate the multifolding Origami manufacture of elastically-deformable Distributed Bragg Reflector (DBR) membranes that reversibly color-tune across the full visible spectrum without compromising their peak reflectance. Multilayer films composed of alternating transparent rubbers are fixed over a 300 mu m wide pinhole and deformed by pressure into a concave shape. Pressure-induced color tuning from the near-IR to the blue arises from both changes in thickness of the constituent layers and from tilting of the curved DBR surfaces. The layer thickness and color distribution upon deformation, the band-gap variation and the repeatability of cyclic color tuning, are mapped through micro-spectroscopy. Such spatially-dependent thinning of the film under elastic deformation produces spatial chirps in the color, and are shown to allow reconstruction of complex 3D strain distributions. (C) 2012 Optical Society of America

Enhancement of the properties of EPDM/NBR elastomers using nanoclay for seal applications

In this research, we have investigated the effects of addition of different percentages of nanoclay to the ethylene propylene diene monomer (EPDM) and nitrile butadiene rubber (NBR) on the characteristics of these rubbers as seal material. Properties such as tensile strength, modulus at different extensions, elongation at break, compressive set, hardness, and permeability and abrasion resistance are tested to assess the effect of addition of the nanoclay. Results indicate that addition of nanoclay at certain compositions could slightly reduce the strength of the rubber. However more stable modulus at different strains are provided, the hardness of the rubber is preserved and slightly enhanced, the permeability is reduced in both rubbers especially considerable decrease in EPDM is observed which is desirable in diminishing the effect of explosive decompression. At the same time the compression test shows that the nanoclay improves the performance of the rubbers under compression which is essential in seal application. The X-ray diffraction tests clarify that the dispersion of the nanoclay in the NBR samples is of high quality. In the EPDM samples, the dispersion is in need of improvement. POLYM. COMPOS., 30:1657-1667, 2009. © 2008 Society of Plastics Engineers.

Hard coatings on elastomers for reduced permeability and increased wear resistance

In this study, three different elastomers, namely hydrogenated nitrile butadiene rubber, fluoroelastomer and silicone, have been subjected to two different hard metallised coatings by ion implantation process. The three different elastomers are commonly used in various seal applications, where reduced wear and gas permeability are essential in maintaining seal performance and functionality. Samples of these rubbers have been coated with chromium coating in one set of tests. In the second set of tests, samples of elastomers have been coated with tungsten carbide coating being deposited on all the three different elastomers. Wear, gas permeability and mechanical behaviour of the coated samples were compared with each other and with the control uncoated elastomers. All the coated samples showed good reduction in gas permeability. With the use of metallised coatings, there has been improved resistance to wear in all the coated samples. Adhesion strength and effect of coating on the elastomer have been investigated by mechanical testing. Mechanical tests revealed good adhesion of metal coatings on all the rubber samples, and there was no detrimental effect on the mechanical properties after coating. © 2012 Institute of Materials, Minerals and Mining.

Instrumental Parasites: Interfacing the Fragile and the Robust

The parasitical relationship between the grand piano and the myriad objects used in its preparation as pioneered by John Cage in the late 1940’s is here discussed from a perspective of free improvisation practice. Preparations can be defined as the use of a “non-instrument” object (screws, bolts, rubbers etc…) to alter or modify the behaviour of an instrument or part of an instrument. Although also present in instrumental practices based on the electric guitar or the drum kit, the piano provides a privileged space of exploration given its large‐scale resonant body. It also highlights the transgressive aspect of preparation (the piano to be prepared often belongs to a venue rather than to the pianist herself, hence highlighting relationships of trust, care and respect). Since 2007 I have used a guitar-object (a small wooden board with strings and pick ups) connected to a small amplifier to prepare the grand piano in my free improvisation practice. This paper addresses the different relationships afforded by this type preparation which is characterised by the fact that the object for preparation is in itself an instrument (albeit a simplified one), and the preparation is ephemeral and intrinsic to the performance. The paper also reflects on the process of designing an interface from and for a particular practice and in collaboration with a guitar luthier.

Propriedades intrínsecas e de processamento de termoplásticos elastoméricos incorporando borracha de pneu reciclada

O trabalho apresentado tem por objetivo contribuir para a valorização da borracha proveniente de pneus em fim de vida, assente em princípios de sustentabilidade ambiental. A abordagem adotada para a concretização deste objetivo consiste na incorporação de borracha de pneus em formulações de base termoplástica e elastomérica (TPE), adequadas ao processo de moldação por injeção. São desenvolvidos estudos sobre a morfologia, propriedades mecânicas, térmicas e reológicas das ligas poliméricas à base de granulado de borracha de pneu (GTR). A falta de adesão entre o GTR e a matriz polimérica leva à degradação das propriedades mecânicas dos materiais obtidos. A estratégia explorada passa pela utilização de um elastómero para promover o encapsulamento do GTR e, desta forma, procurar obter ligas com propriedades mecânicas características de um TPE. São analisadas ligas ternárias (TPEGTR) compostas por polipropileno (PP) de elevada fluidez, GTR e elastómero virgem. O efeito da presença de diferentes elastómeros nas ligas é analisado neste trabalho: um elastómero de etilenopropileno- dieno (EPDM), e um novo elastómero de etileno-propileno (EPR) obtido por catálise metalocénica. O estudo da morfologia das ligas obtidas mostra haver interação entre os materiais, sendo possível inferir a viabilidade da estratégia adotada para promover a adesão do GTR. A incorporação de elastómero promove o aumento da resistência ao impacto e da extensão na rotura nas ligas, o que é atribuído, fundamentalmente, ao encapsulamento do GTR e ao aumento da tenacidade da matriz termoplástica. Com o objetivo de avaliar a influência da estrutura cristalina das ligas TPEGTR no seu comportamento mecânico, procede-se à análise do processo de cristalização sob condições isotérmicas e não isotérmicas. Neste estudo, é avaliado o efeito da presença dos materiais que constituem a fase elastomérica na cinética de cristalização. Para cada uma das ligas desenvolvidas, recorre-se ao modelo de Avrami para avaliar o efeito da temperatura no mecanismo de nucleação, na morfologia das estruturas cristalinas e na taxa de cristalização. Recorre-se à reometria capilar para estudar, sob condições estacionárias, o comportamento reológico das ligas TPEGTR. O modelo de Cross-WLF é utilizado para avaliar o comportamento reológico de todos os materiais, obtendo-se resultados similares àqueles obtidos experimentalmente. O comportamento reológico dos polímeros PP, EPR e EPDM é do tipo reofluidificante, tendo o EPR um comportamento reológico similar ao do PP e o EPDM um comportamento reo-fluidificante mais pronunciado. Em todas as ligas analisadas o comportamento reológico revela-se do tipo reo-fluidificante, sendo que a presença de GTR promove o aumento da viscosidade. Os parâmetros obtidos do modelo de Cross-WLF são utilizados para realizar a simulação da etapa de injeção recorrendo a um software comercial. Os resultados obtidos são validados experimentalmente pelo processo de moldação por injeção, evidenciando uma boa adequabilidade da aplicação deste modelo a estas ligas. O trabalho desenvolvido sobre ligas TPEGTR, constitui um contributo para a valorização da borracha proveniente de pneus em fim de vida, assente em princípios de sustentabilidade ambiental.

Receipt to S.D. Woodruff from T. Healey

Receipt to S.D. Woodruff from T. Healey of St. Catharines, dealers in Boots, Shoes, Rubbers and Gaiters regarding shoes and shoe repairs, Jan. 1, 1876.

Studies on Rubber Composition as Passive Acoustic Materials in Underwater Electro Acoustic Tranducer Technology and Their aging Characteristic

The research work has been in the area of compounding and characterization of rubbers for use in under water electro acoustic transducers. The study also covers specific material system such as encapsulation materials, baffle material, seal material, etc. Life prediction techniques of under water rubbers in general have been established with reference to more than one functional property. Ranges of passive materials, besides the active sensing material go into the construction of underwater electro acoustic transducers. Reliability of the transducer is critically dependent on these passive materials. Rubbers are a major class of passive materials. The present work concentrates on these materials. Conventional rubbers are inadequate to meet many of the stringent function specific requirements. There exists a large gap of information in the rubber technology of underwater rubbers, particularly relating to underwater electro acoustic transducers. This study is towards filling up the gaps of information in this crucial area. Water intake into rubber is considered as the single most important issue for the long-term performance of rubbers, especially Neoprene. In this study, the cause and effects of a range of parameters affecting the water absorption by diffusion and permeation have been investigated.